A Complementary Metal-Oxide Semiconductor (CMOS) technology and a technique thereof are widely applied to the field of computers. An Active Pixel Sensor (APS) serves as the most common CMOS camera detection circuit, and a specific circuit of such an APS pixel circuit is as shown in FIG. 1.
As shown in FIG. 1, the APS pixel circuit is formed by a switching transistor T1, a switching transistor T3, a driving transistor T2 and a photodiode PD, and the driving transistor T2 serves as a source electrode follower. When exposure begins, the switching transistor T1 is turned on under control of an initialization signal (Reset) input by an initialization signal end, the photodiode PD is reversely biased to a voltage Trst, and the voltage Trst charges a PN junction capacitor of the photodiode PD. When incident light illuminates on a PN junction of the photodiode PD, light quantum excitation generates electron-hole pairs on the PN junction, such that charges on the PN junction capacitor are recombined, causing a gate electrode potential of the driving transistor T2 to be reduced. Finally, the switching transistor T3 is turned on, a size of a photocurrent at this point is determined from an output signal line 10, and current illumination in front of a camera is ultimately determined according to the size of the actually measured photocurrent.
From FIG. 1, it can be seen that in existing technologies, a current read by the output signal line 10 is related to a threshold voltage of the driving transistor T2, while in an actual manufacturing process, due to technological manufacture procedures and long time operation of the driving transistor T2, drift of a threshold voltage Vth of the driving transistor T2 may be caused. As a result, there exists a difference between the size of a current finally output and the size of a current actually generated after illumination on the photodiode PD, and distortion of a display image is thus generated.
In conclusion, in existing technologies, due to the drift of the threshold voltage of the driving transistor, there exists a difference between the size of the output current and the size of the current actually generated by illumination.